Testing device for acoustical logging system



July l2, 1960 R. J. LOFBOURROW TESTING DEVICE FOR ACOUSTICAL LOGGINGSYSTEM Filed Feb. 6, 1956 Robert J. Loofbourrow, Bellaire, Tex., assgnorto Texaco Inc., a corporation of Delaware Filed Feb. 6, i956, sei-(N0.563,579

11 Claims. (ci. isi-.5)

This invention relates to acoustical well logging ap'- paratus and moreparticularly to a device for testing an acoustical velocity loggingsystem.

It has been proposed heretofore to survey Wells or earth bores bygenerating sound or acoustic waves at a given level in a well and thenmeasuring the velocity of sound propagation through the surroundingearth strata thereby to determine the acoustic propertiesV of thestrata. The determinations may be made at a number of different levelsso as to ascertain the variation in acoustic properties of the stratathroughout the entire'depth of the well. The velocity of sound through-a given stratum may be determined by 'measuring the time difference orlapse between the instant of transmission and the instant of receptionof a sound wave or pulse. Thus, if the trans` mitter and receptor areseparatedfa known'distance d,

where v is ,equalito `thevelocity of 'soundpropagation,V

d is equal to the Vdistance of travel 'of the sound wave and li is equalto: the time of travel of the wave. As

`indicated by the foregoing equation, the velocity of sound propagation-is inversely proportional to the time of travel. v The velocity ofYsound propagated through a given stratum surrounding an earthV bore mayalso Abe determined by transmitting a pulse of acoustic energy ata givenlevel and then measuring the time dilerential bei tween the instant ofdetection of the pulse by each of two receptors spaced a iixed distanceapartin the earth Inlmy copending U.S. patent pplication favor of acontinuation application having Serial No.

`574,844, filed March 29, 1956,'1 have'described my acoustical velocitylogging `systemiyhichincludes a transducer for transmitting acousticenergy and two transducersior` receiving the transmittedacousticenergyand fon converting it intocorresponding electrical wavesor pulses. 4This device also includesfa time measuring circuit fordetermining'the time diierence between theinstant of detection of agiven pulse of acoustic energy at one receiving transducerV and theinstant of Vdetection ofv 1 that pulse at the second receivingtransducer and means for recording this timeV diiierence, or, byconversion, theV velocity of propagation of the sound wave, againstw'elldepth. My acoustical velocity logging system. further 1ncludesa tool orsonde for housing the transmitting trans-A having Serial No. l57,495,iiled April 22, 1950, now abandoned inV States Patentl 2,944,621' -YPatented `July 12, 1950 .ICC

structure attached to a conductor cable for passing eleo-A trical energyto and from the tool and for suspending or supportingV the tool in theearth bore. Each transducer is mounted in the tool so that it may bereadily coupled to the earth strata surrounding the bore through thehuid or mud in the bore.

It is an object of this invention to produce a device for testing theoperative condition of an acoustical velocity logging system.

It is another object of this invention to produce a testing device whichwill enable an operator of an acoustical velocity logging system to testthe logging system thoroughly without having to open the shell or casingof the tool. Y

It is a further object of this invention to produce a simple testingdevice which Will more quickly enable'an operator Ito test hisacoustical Well logging system than with the use of standard electricaltest equipment such as an oscilloscope.` Y

ln accordance with the present invention and in one form thereof thereis provided an acoustical testing device which includes a receivingtransducer for converting acoustic energy into first electric energy,means responsive to the'electric energy for producing delayed Yelectricenergy at a predetermined time after the arrival thereat of the iirst'electric energy and a transmitting transducer for converting thedelayed electric energy into second vacoustic energy. The testing devicemay addi'- tionally include means responsive to thedelayed electricenergy for producing'second delayed electric energy at a predeterminedtime'after the arrival thereat of theA first delayed lelectric energyand a second transmitting .Y

transducer converting the second'delayed electric energy into thirdacousticenergvf Y i Fora more complete understanding or the presentinvention reference may now be had Vto the following;

description taken Yin conjunction with the accompanying drawing wherein:f

iThe ligure schematically illustrates in block form a testing device in`accordanceA with this invention anda portion of the tool or sonde of anacoustic velocity log-- ging system employing one transmitter and tworeceivers. v Referring to the iigure in more detail, the-toolor sonde 10of an acoustical velocity logging systemof the type described in myabove-mentioned copending application includes one transmittingtransducer 11 land two receivingtransduers 12 ,and 13. The testingdevice `14- includes a receivingtransducer 15 which may be convenientl'y directlyfcoupled tothe transmitting transducer 11'of the tool1th. The receiving transducer 15 detects acoustic pulses transmitted bythe transmitting transducer- 171 of the tool 10 and converts theselacoustic pulses into isY generated by Vmultivibrator 19 and fed intothe diieren-V `tilator 20 for deriving alfsharpgpulse from the trailingedge fof the square wavewhich is then amplified by amplier d'icer andthe two receiving transducersv and for main?" t taining the transducersat fixed distances from each other.` i The toolfhas the form of anelongated cylindrical closed lshell of relatively small diameter suchthat it can be ztoa secondf'delayed pulse unit 24 which .may also, for f2 1,` preferably having a cathode follower outputproducv 'ing a signalof iixed amplitude. .The Xed amplitude sig-'1V nal 'is then` fed into acalibrated attenuator '22 before'y being appliedto afirst transmittingtransducer 2,3 which is'adapted to be'readily' directly coupled to thereceiving transducer 12 of the Well logging tool 10.

' The sharp pulse derived from ditterentiatorzt), in addition to beingapplied tothe ampliiier 21, is also applied 3 example, comprise anadjustable delay one shot or monostable multivibrator 25 and adiierentiator 26. A square wave voltage is generated by multivibrator 25and fed into the differentiator 26 for deriving a sharp pulse from thetrailing edge of the square wave generated by multivibrator 25. Thispulse is then amplified by amplifier 27r which preferably has a cathodefollower output producing a signal of fixed amplitude. The fixedamplitude signal from amplifier 27 is fed into a calibrated attenuator23 jbefore being applied to a second transmitting transducer 29 which isadapted toV be readily directly coupled tothe receiving transducer 13 ofthe well logging tool. 10. Each of the above-,mentioned transducers may,for example, comprise a magnetostrictive element or a piezoelectriccrystal, such as an ammoniumdihydrogen phosphate (ADP) type crystal.

In the operation of the testing device, the receiving transducer 15 ofthe device 14 is directly coupled to the transmitting transducer 11 ofthe tool 10, the first transmitting transducer 23 and the.secondtransmitting transducer I29 ofthe device 14 are coupled toreceiving transducers 12 and l13, respectively, of the tool of theacoustic well logging system under test. A liquid or oil film may beused at the interface of the coupled transducers to improve the acousticcoupling therebetween. When a pulse is transmitted from the transmittingtransducer 11 of tool 10, the receiving transducer 15 of the testingdevice 14 detects this pulse and converts it into an electric pulsewhich after amplification by amplifier 16 fires the gas trigger tube 17to produce a single sharp pulse which initiates theoperation of thedelayed pulse unit 1,8 and more particularly the multivibrator 19 whichproduces Va square wave having a duration o r width determined by thetime constants of themultivibrator, as is well known by those slgilledin the art. The square wave is` then` differentiated by diferentiator 20whichproduces a sharp pulse which is applied to channels leading to boththe first and second transmitting transducers 23Y and29 of the testing`device 14; s The sharp p ulse derived from the differentiated trailingedge of the square wave from multivibrator 19 is applied to the firsttransmitting transducer via amplifier 221, which preferably has acathodefollower output producing a fixed amplitude signal, and a calibratedattenuator 22. This same sharp pulse which is derived from diierentiator2t) is also applied to the. delayed pulse unit 24, operating in,substantially the same manner as delayed pulse unit 15 forproducing adelayed pulse which is amplified by amplier 27, also preferably having acathode follower output producing a .signal of fixed amplitude. Thepulse from amplifier 27 is then attenuated by calibrated attenuator .28before being applied to the second, transmitting transducer 29. Delayedpulse units` 18 andv 24 may each have a calibrated adjustable delaymultivi-` brator, however, since the time measuring circuitof theAacoustic velocity logging system having tool 10 is` responsive only. tothe pulses detected at its receivers 12 and 13, only delayed pulse unit24 of the testing device need be calibrated. However, when testing asystem which has only one receiver, second delayed pulse unit 24, secondamplifier` 2'7, second calibrated attenuator 28 and second transmittingtransducer 29' are not needed, but in that, event the multivibrator 19of delayed pulse unitA 18 should be calibrated.

`It can readily Abe seen that the delay time of a pulse from delayedpulse Vunit 2.4 canbe made, to equal the interval of time required foran acoustic pulse from transmitting transducer 11 of -tool 10 totravelin avparticular stratum surrounding an earth bore between. receivingvvtransducers 12 and 13 of the tool 10. Furthermore, it

notfbencalibratedsince a two; receiver acousticgvelocity 4 loggingsystem would not ordinarily record the time required for an acousticpulse to travel from its transmitting transducer to the first receivingtransducer. However, it is desirable to utilize a delayed pulse unitbetween the receiving transducer 15 and the first transmittingtransducer 23 in order to determine whether spillover pulses betweentransmitting transducer 11 and receiving transducer 12 of tool 10 areinterfering with the proper operation of the acoustic velocity loggingsystem. The delay time of the delayed pulse unit 18 of coursecorresponds to the interval of time required for an acoustic pulse fromtransmitting transducer 11 to reach receiving transducer 12.

Calibrated attenuators 22 and 28 have been inserted into the testingdevice in order to determine the minimum signal which can be detected bythe receivers 12 and 13 of tool 16. The minimum signal from the testingdevice 14 which will-operate the receiver circuits of tool 10 is ameasure of the sensitivity of each of the receiver circuits. If during atest of an acoustic velocity logging system the attenuator settingindicates that a considerably stronger signal than the minimum signal isrequired to operate the logging system it can reasonably be presumedthat the system is not in proper working condition.

Accordingly, this invention provides an acoustical testing device whichenables an operator to test his acoustical velocity logging systemthoroughly without even having to open the tool casing or shell and morerapidly than with the use of standard electrical test equipment such asan oscilloscope. This testing device produces apparatus which is capableof checking the sensitivity of each channelV ofthe well logging systemand the operation and accuracy of the velocity indicating equipmentwithin the tool casing up to and including the surface indicatingequipment of the system. A further test can enable the operator to checkthe system circuitry for a full range of velocities over which thecircuits must operate satisfactorily by properly varying the timeconstant ofthe calibrated multivibrator. The knowledge that anacoustical velocity logging system is not functioning properly before itis -lowered into the earth bore is well appreciated by.

' said acoustic energy producing means for converting saidacoustic-energy into rst electric energy, means responysive tosaidelectric energy for producing delayed elec- 'tric energy at .apredetermined time after the arrival thereat of said first electricenergy, an acoustical transmitting transducer operatively coupled tosaid acoustic energy receiving means at a point spaced from saidacoustical receiving transducer for converting said delayed electricenergy into second acoustic energy for transmission-to the receivingmeans of the acoustical velocity logging system and acalibrated-attenuator interposed between said delayed electric energyproducing ymeansy and said transmitting transducer for controlling ythestrength of the delayed electric energy applied to said Itransmittingtransducer.

s v2,. An acoustical testing device for testing the opera- ,tion of anacoustical velocity logging system which has lmeans for Yproducingacoustic energy and first and second means for-receiving acousticenergy, said device comprising an acoustical receiving transducerconverting said acoustic energy into first electricV energy, meansresponsive ltosaid electric energy for producing delayed electricenergyat apredetermined' time after the arrival thereat of said iirst electricenergyfa rst acoustical transmitting transducer convertingsaid delayedYelectric energy into second acoustic energy `for transmission tothe rst,receiving means of the acoustical velocity logging system and a iirstcalibrated Vattenuator interposed between said delayed electric energyproducingmeans and said first transmitting transducer for' controllingthe strength of the delayed electric energy applied to said rsttransmitting transducer, means responsive to said delayed electricenergy for producing second delayed electric energy at a predeterminedtime after the arrival thereat of said first first delayed electricenergy, a second' acoustical transmitting transducer converting saidsecond delayed electric energy into third acoustic energy fortransmission to the second receiving means .of jthe :acousticaldoggingsystem and a second calibrated. attenuator interposed between the seconddelayed electric producing means and said second transmitting transducerfor controlling' the strength of the second delayed electricrenergy tosaid second transmitting transducer.

3. An acoustical testing device for testing the opera- ,tion of anacoustical velocity well logging system which has means for producingacoustic energy and means for receiving acoustic energy, said devicecomprising an acoustical receiving transducer operatively coupled tosaid acoustic energy producing means for converting said acoustic energyinto electric energy, a delayed pulse unit responsive to said electricenergy for producing a delayed pulse at a predetermined time after thearrival thereat of said electric energy and an acoustical transmittingtransducer operatively coupled to said acoustic energy p receiving meansat a point spaced from said acoustical ,acoustical receiving transducerconverting said acoustic energy into iirst electric energy, a firstdelayed pulse unit responsive to said electric energy for producing afirst delayed pulse at a predetermined time after the arrival thereat ofsaid electric energy, a first acoustical transmitting transducerconverting said delayed pulse into a Vfirst acoustic pulse fortransmission to the first receiving means Iof the acoustical velocitylogging system, a second delayed pulse unit responsive to said iirstdelayed pulse for producing a second delayed pulse at a predeterminedtime after the arrival thereat of said first delayed pulse and a secondacoustical transmitting transducer converting said seconds' delayedpulse into a second acoustic pulse for transmission` to the secondreceiving means of the acoustical velocity logging system. Y

6. An acoustical testing device as set forth in claim `wherein saidsecond delayed pulse unit comprises a calibrated adjustable delaymultivibrator and a dierentiator coupled to the output of saidmultivibrator.

7. An acoustical testing device for testing the operation of anacoustical velocity logging system which has means for producing anacoustic pulse and means for receiving an acoustic pulse, said devicecomprising a receiving transducer Yconverting said acoustic pulse into afirst electric pulse, means for amplifying said iirst electric pulse, .agas trigger tube responsive to said amplified electric pulse forproducing aV sharp electric pulse, a

delayed pulse unit responsive to said sharp pulse for prot ducing adelayed pulse at a predetermined time after the arrival thereat of saidsharp pulse, said delayed pulse comprising a calibratedadjustable delaymultivibrator and a diierentiator coupled tothe output of saidmultivibrator, an, amplifier having an output producing a fixedamplitude pulse for amplifying said delayed pulse, Ia calibratedattenuator for controlling the amplitude of lsaid fixed amplitude pulseand a transmitting transducer ,converting the pulse from said attenuatorvinto a second Iacoustic pulse for transmission to the receiving meansof the acoustical velocity logging system.

8. An acoustical testing device Ifor testing the operation of anacoustical velocity logging system which has means for producing anacoustic pulse and iirst and second means for receiving an acousticpulse, said device comprising a receiving transducer converting saidacoustic pulse into a first electric pulse, an amplifier for amplifyingsaid irst electric pulse, a gas trigger tube responsive to said 'ampliedfirst electric pulse for producing a sharp `electric pulse, a iirstdelayed pulse unit responsive to said sharp electric pulse for producinga first delayed pulsev at apredetermined time after the arrival thereatof said sharp electric pulse, said first delayed pulse unit comprisingan adjustable delay multi vibrator and a iirst diierentiator coupled tothe output of said multivibrator, a first amplifier having an outputproducing a fixed amplitude pulse for amplifying said first delayedpulse, a Iirst calibrated attenuator for varying the amplitude of saidfixed amplitude pulse, a first transmitting transducer converting thepulse from said first calibrated attenuator into a second acoustic pulsefor transmission to the iirst receiving means of the acoustical velocitylogging system, a second delayed pulse unit responsive to said iirstdelayed pulse for producing a second delayed pulse at a predeterminedtime after the. arrival thereat of said first delayed pulse, said seconddelayed pulse unit comprising a calibrated adjustable delaymultivibrator and a second diferentiator coupled to the output of saidcalibrated multivibrator, a second amplifier havingv an output producinga fixed amplitude pulse for amplifying said second delayed pulse, asecond calibrated attenuator for varying the amplitude of said iixedamplitude pulse from said second amplier and a second transmittingtransducer for converting the pulse Ifrom said second attenuator into athird acoustic pulse for transmission to the second receiving means ofthe acoustical velocity logging system.

9. An acoustical testing device for testing the operation of anacoustical velocity logging system which has means 4for producingacoustic energy and means for receiving acoustic energy, said devicecomprising a receiving transducer converting said acoustic energy intoelectric energy, a delayed pulse unit responsive to said electric energyfor producing a delayed pulse at a predetermined time after the arrivalthereat of said electric energy, an amplifier having an output producinga pulse of txed amplitude for amplifying said delayed pulse, acalibrated attenuator coupled to the output of said amplifier forcontrolling the'amplitude of the tixed amplitude pulse from saidamplifier and for producing a `calibrated pulse and a transmittingtransducer converting said calibrated pulse into an acoustic pulse fortransmission to the receiving means of the acoustical velocityV loggingsystem.

10. An acoustical testing device for testing the operation of anacoustical velocity logging system which has means for producingacoustic energy and first and second means for receivingacousticrenergy, said device cornprising a receiving transducerconverting said acoustic energy into first electric energy, a firstdelayed pulse unit responsive to said electric energy for producing aiirst delayed pulse at a predetermined time after the arrivalthereat ofsaid electric energy, a first ampliiier having an output producing afixed amplitude pulse for amplifying said first delayed pulse, a firstcalibrated attenuator coupled to the output of said first amplifier forcontrolling the amplitude of said xed amplitude pulse and for producinga first calibrated pulse, a first acoustianoniem `cal' 'transmitting Itransducer converting said calibrated "pulse into a firstv acousticpulse yfor transmission to t-he first receiving means-of theacoustical=veloitylogging system, a second delayed pulse unit responsive-to Ysaid rst delayed pulse lfor producing a second delayed pulse at apredetermined time after the arrival 'thereatof said '-rst delayedpulse, a second amplifier havinglian 'output lproducing a iixedamplitude pulse forvamplifying said -said second amplier andforproducing a second caliv'br-ated pulse and a secondtransmitting-transducerfconverting said second calibrated pulseintoa`=seoo11`d acoustic pulse yfor transmission to thesecond'rece'iv-ing meansfof the acoustical velocity logging system.

1.1. Apparatus for testing lan 'acoustical velocitywell logging systemhaving van elongated exploringI tool which indicates vthe time of travelof an acoustic wavefbetween two spaced' transducers on saidtool'comprisingmeans operatively kcoupled tosaid tool at'fone of saidtwo transducers for producing 'a Vrst electric pulse indicative of theoccurrence of acoustic energy at said one transducer, means responsiveto said first `pulse producing means for producing a -second Yelectricpulse at a predetermined time vafter said rst pulse is produced andmeans responsive to said second pulse producing means and operative- 1ycoupled to said tool at the other of said two trans- 'ducers forconverting lsaid second pulse into acoustic energy --for transmission to.said tool at said other transducer.

ReferencesrCited in the tile of this patent UNITED STATES PATENTS1,540,317 Craft et al. June 2, 1925 2,275,736 Cloud Mar. 10, 19422,477,485 Jacob -uly 26, 1949 2,505,525 Clapp et a1. Apr. 25, 1950'2,704,364 Summers Mar. 15, 1955

